Occurrence of a Cavity‐Nesting Tropical Swallow Is Associated to Riverbed Lithology

Understanding the factors shaping species distribution is a key challenge in ecology and biogeography. While dispersal limitations, environmental features, and biotic interactions are commonly recognized as key determinants of species abundance and distribution, some species exhibit patchy distributions that remain hard to explain. Here, we examined the influence of geological features and land‐use type in shaping the patchy distribution of Black‐collared Swallows ( Pygochelidon melanoleuca ) in southeastern Brazil. This swallow is a microhabitat specialist, restricted to rocky torrents, where it nests within cavities in rock outcrops along the riverbed. We hypothesized that riverbed lithology is a major environmental feature driving this species' occurrence in southeastern Brazil, particularly through the presence of rocks that form suitable nesting cavities. Occurrence data from the literature, citizen science platforms and a field survey along 250 km of the Paraopeba River revealed an association between the species' presence and riverbed areas dominated by metasedimentary rocks from the Bambuí Group. In contrast, the species was absent from regions underlain by Archean crystalline rocks, which produce less suitable nesting sites. These findings suggest that riverbed lithology is a primary factor shaping the distribution of the Black‐collared Swallow, emphasizing the role of geological features in driving species habitat suitability. Land‐use type also influenced the species' occurrence, with Black‐collared Swallows favouring areas covered by native vegetation. Further research is needed to assess the generality of these patterns for this species across other river systems in South America.